1. Mr. Christopher Briner Unit 1.1 Cell theory
KIS International School
IB DP Biology
Unit 1.1
Cell theory

2. 1.1.U1
According to the cell theory, living organisms are composed of cells.

3. Cell Theory Cells are the smallest units of life
Living organisms are composed of cells
Cells come from pre-existing cells

4. Cell Theory
A theory is a general system of ideas used to explain or interpret observations
Theories provide predictive power by generating hypotheses
A hypothesis is a specific prediction that can be tested through observation or experiment

5. Just theories? TOK QUESTION:
How much evidence is needed for a hypothesis to become a theory? Should a theory be abandoned when there is evidence that it does not offer a full explanation?

6. Cell Theory
Each aspect of cell theory is based on evidence obtained through observations and experiments

7. Cell Theory Evidence Cells are the smallest units of life
Nothing smaller than a cell can survive independently
Subcellular structures (nuclei, ribosomes, etc.)
Lower limit on cell size is about 200nm
Large enough for DNA, membranes, etc.

8. Cell Theory Evidence All living things are made of one or more cells
Microscopes allow us to observe that all living things are composed of cells
Either unicellular or multicellular

9. Cell Theory Evidence All cells come from pre-existing cells
Prokaryotes reproduce by binary fission
Eukaryotes reproduce by mitosis
All cells then have a common ancestor
Implies that all cells are related

10. Cell Theory Evidence All cells come from pre-existing cells
Geology implies life hasn’t always existed
Life originated 1 billion years after earth

11. 1.1.A1
Questioning the cell theory using atypical examples, including striated muscle, giant algae and aseptate fungal hyphae.

12. Cells
What is a cell?
A functional unit of cytoplasm surrounded by a membrane and containing genetic material
Not all cells meet this definition

13. Cells What is a cell? Exceptions:
Striated muscle, fungal hyphae, and some algae have cytoplasms that are multi-nucleated
Challenges idea that cells have one nucleus
Giant algae have one nucleus, but are huge!
5-100 mm
Challenges idea that cells are small

14. Cells What is a cell? Exceptions:
Connective tissue is composed of both cellular and extracellular structures
But they are a product of cellular activity
Organisms are made up of cells and modified cells and cell products
This modification is called Organismal Theory

15. 1.1.U2
Organisms consisting of only one cell carry out all functions of life in that cell.

16. Cells Unicellular organisms carry out all the functions of life:
Growth
An irreversable increase in size
Homeostasis
Keeping conditions inside the organisms within tolerable limits
Metabolism
Chemical reactions inside the cell
Including cell respiration to release energy

17. Cells Unicellular organisms carry out all the functions of life:
Nutrition and Excretion
Obtaining food to provide energy and the materials to grow, then getting rid of waste products
Reproduction
Producing offspring either sexually or asexually
Response
Perceiving and responding to changes in the environment

18. Cells
MR H GREN

19. 1.1.A2
Investigation of functions of life in Paramecium and one named photosynthetic unicellular organism.

20. Cells

21. Cells

22. 1.1.S1
Use of a light microscope to investigate the structure of cells and tissues, with drawing of cells. Calculation of the magnification of drawings and the actual size of structures and ultrastructures shown in drawings or micrographs. (Practical 1)

23. Cells Units of size mm = millimeter = 10-3 meters
μm = micrometer = 10-3 millimeters
nm = nanometer = 10-3 micrometers

24. Cells

25. Cells Important scales 1 nm = molecules
10 nm = cell membrane thickness
100 nm = viruses
1 μm = bacteria
1 – 10 μm = organelles
10 – 100 μm = eukaryotic cells
MTV Beats Other Channels!

26. Cells Calculating magnification
Magnification = size of image / real size
Drawing of microscopic structures must include:
Scale bars: | | = 10 nm
Magnification: x 500

27. TOK QUESTION:
So small….
Nearly all these biological entities are beyond our ability to perceive directly. One must use technology to ‘see’ them.
Should a distinction be made between knowledge claims dependent upon observations made directly with the senses and knowledge claims dependent on technology or maths?

28. 1.1.U3
Surface area to volume ratio is important in the limitation of cell size.

29. Cells Surface Area: Volume ratio Surface Area Volume (SA) = f(x2)
Rate of exchange = f(SA)
Volume
(V) = f(x3)
Metabolism = f(V)
Includes heat and waste production and resource consumption

30. Cells Surface Area: Volume ratio Therefore:
V increases faster than SA when the dimensions of a cell increase
SA:V ratio decreases with growing cell size

31. Cells Surface Area: Volume ratio
As the organism gets bigger, its SA: V ratio decreases
This rule is a limiting factor for cell size
As the cell gets bigger the ratio decreases
If the ratio decreases the rate of exchange decreases

32. Cells Surface Area: Volume ratio Example: Oxygen for respiration
A cell respiring aerobically needs oxygen
Oxygen is obtained from the surrounding environment
Such as water or blood (depends on the cell)
Oxygen diffuses across the cell membrane.
More membrane allows more diffusion

33. Cells Surface Area: Volume ratio Example: Oxygen for respiration
Ratio of SA:V decreases in bigger cells
Volume of oxygen obtained for each unit of cell volume is actually decreasing
Cells must not get too big because they cannot obtain sufficient oxygen to satisfy the demands of the cell.

34. Cells Surface Area: Volume ratio Therefore:
Sets an upper limit on cell size
Low SA reduces rate of exchange
High V increases metabolic demands
Oxygen, nutrients, wastes, etc.
Low SA:V means rate of exchange can not meet metabolic demands

35. 1.1.U4
Multicellular organisms have properties that emerge from the interaction of their cellular components.

36. Cells Cells are emergent Whole is greater than the sum of its parts
Arises from the interaction of component parts
Life itself can be viewed as an emergent property

37. Cells Cells are emergent Example: Light bulb
Bulb made of several parts
We can individually study the properties of :
Tungsten
Metal cup
Glass container
Does not allow the prediction of the lightbulb
Only combine them can this property be found

38. TOK QUESTION: Emergent-cy?
The emergent nature of life raises many questions… When should death be defined? Most human cells are still alive long after the heart stops beating.

39. 1.1.U5
Specialized tissues can develop by cell differentiation in multicellular organisms.

40. Cells Differentiation Unicellular organisms Multicellular organisms
Must solve all of life’s challenges in a single cell
Multicellular organisms
Can differentiate into different types of cells
Each type can be specialized for certain functions, increasing efficiency
Division of labor

41. 1.1.U6
Differentiation involves the expression of some genes and not others in a cell’s genome.

42. Cells Differentiation Achieved through differential gene expression
All cells in an organism have identical DNA
Different cell types make different proteins
A result of transcription regulation
Each cell type expresses a subset of its genome
“turning on” some genes and “turning off” others

43. 1.1.U7
The capacity of stem cells to divide and differentiate along different pathways is necessary in embryonic development and also makes stem cells suitable for therapeutic uses.

44. Cells
Stem cells
Stem cells can
Divide
Differentiate
Specialize

45. 1.1.A3
Use of stem cells to treat Stargardt’s disease and one other named condition.

46. Cells In Stargardt’s disease:
Causes blindness due to dying retina cells
Embryonic stem cells obtained
These are injected into the eye of patient
Cells attach to patient’s retina and differentiate into healthy cells.

47. Cells In lymphoma or leukemia:
Cells are removed from the bone marrow of the patient
High doses of chemotherapy drugs kill dividing cells in patient
Both cancerous and normal cells die
HS Cells from the marrow are transplanted back into the patient
Fully restores the production of healthy blood cells and marrow

48. Cells Stem cells: Therapeutic use
Bone marrow transplants use hematopoietic stem cells (HS cells)
Found in bone marrow and produce red and white blood cells
100 HS cells can completely replace the blood system of mice after all their marrow has been destroyed

49. 1.1.A4
Ethics of the therapeutic use of stem cells from specially created embryos, from the umbilical cord blood of a new-born baby and from an adult’s own tissues.

50. Cells Stem cells: Ethical issues
Use involves death of early-stage embryos
Therapeutic cloning could reduce suffering in a wide variety of conditions

51. TOK QUESTION: Stem Cells
Do the potential medical benefits of research on human embryos justify their use? What can we use them for and how can we get them? How old can they be?
Should stem cells be used even though they can potentially turn into tumors?

52. MAJOR SOURCES
Thank you to my favorite sources of information when making these lectures!
John Burrell (Bangkok, TH)
Dave Ferguson (Kobe, JA)
Stephen Taylor (Bandung, IN)
Andrew Allott – Biology for the IB Diploma
C. J.Clegg – Biology for the IB Diploma
Weem, Talbot, Mayrhofer – Biology for the International Baccalaureate
Howard Hugh’s Medical Institute –
Mr. Hoye’s TOK Website –
And all the contributors at